Multi-component molecular crystals, which include salts, co-crystals and solvates, represent a promising route to new functional materials. [1] In principle, supramolecular synthons and the ideas of crystal engineering can be used to bring co-formers together in the crystal, and ultimately design a material with particular desirable properties. In order to do this effectively, the interactions between the molecules, as well as how these might be influenced by the crystallisation process, must be understood.
The 1,2,3,5-dithiadiazolyl radicals (DTDAs), R-CNSSN•, are of considerable interest due to their potential as building blocks for materials with interesting magnetic or conducting properties, but DTDAs frequently dimerise in the solid state via an interaction known as pancake bonding, rendering them diamagnetic. Our efforts to understand the nature of the pancake bonding between dithiadiazolyl radicals in the solid state will be described, including high resolution X-ray diffraction studies [2] as well as high-pressure crystallography. We have also studied co-crystal formation with dithiadiazolyl radicals, as well as host-guest systems involving this family of radicals. [2,3]
In our efforts to understand multi-component crystals, our group has investigated both mechanochemistry and sublimation as alternatives to solution crystallisation. Sublimation in particular remains an under-utilised technique for the crystallisation of molecular materials. [5] Our group has shown that co-crystals and salts can be selectively crystallised from the gas phase by changing the sublimation conditions. [6] We have also investigated the sublimation of hydrates, [7] as well as the competition between hydrogen and halogen bonding in the gas phase. [8]
These results add to our understanding of the behaviour of multi-component crystals, and how they can be controlled to yield desired crystal forms.